1. Field of the Invention
The present invention relates to optical pumping using depolarizing filters, and more particularly, to systems and methods for optical pumping of a signal through depolarizing filters within an optical amplification system.
2. Description of the Prior Art
New markets and uses are constantly being developed to take advantage of the benefits of optical communications. However, to take advantage of these benefits, optical communications often require systems that inject optical pump signals into an optical fiber to amplify optical data signals. An example of such a system includes a Raman amplifier which amplifies a desired communications signal and prevents communications signal attenuation. In spite of these benefits, however, the cost of components in a Raman amplifier may be prohibitive.
FIG. 1 is an illustration of a distributed Raman amplifier in the prior art. In FIG. 1, an optical signal path 110 receives an input optical signal. Splitter 120 splits the input optical signal. The management system 130 receives and monitors the split input optical signal. Raman pump module 160 pumps an optical pump signal. The optical pump signal is at a higher energy than the input optical signal. Multiplexer/isolator 150 receives and isolates the optical pump signal. The multiplexer/isolator 150 then multiplexes the optical pump signal with the input optical signal into the optical fiber 140 to produce Stimulated Raman Scattering. The photons of the optical pump signal scatter off the vibrating atoms of the optical fiber 140 resulting in electromagnetic stimulation (i.e. Stimulated Raman Scattering) which adds energy to, and thereby amplifying, the input optical signal.
One problem with the distributed Raman amplifier 100 is that a high energy optical pump signal at a specific wavelength must be generated to produce Stimulated Raman Scattering. Optical pump lasers are often used to generate high energy optical pump signals. Optical pump signals generated by optical pump lasers are strongly polarized.
In order to increase the needed power near a specific wavelength, two polarizations orthogonally mixed are utilized. Increasing the optical pump power at a specific wavelength allows the pump signal spectrum to be more equalized as the gain profile in amplification in not uniform. The polarizations are mixed so as to not concentrate too much power at one wavelength and polarization which might cause non-linear effects in standard-type fiber deployed widely in networks today.
One solution to this problem at specific wavelengths needing increased pump power is to generate two initial optical signals at the same wavelength but with orthogonal polarizations. The two initial optical signals are then coupled and their polarizations combined to form an optical pump signal which is then multiplexed into the optical fiber 140 with the input optical signal.
FIG. 2 is an illustration of a Raman pump module 200 in the prior art. At least two pump lasers at wavelength (1) 210 generate separate initial optical signals. Each initial optical signal has a polarization, as does every other initial optical signal of a specific wavelength. The polarization beam combiner 220 couples the initial optical signals of the same wavelength and then combines their polarizations orthogonally. A wavelength division multiplexer (WDM 230) multiplexes the initial optical signals to form an optical pump signal. WDM 230 then transmits the optical pump signal band into optical fiber 240.
In this technique, multiple optical pump lasers are required for certain wavelengths to generate the desired effect of amplification which increases cost. Further, the use of multiple optical pump lasers for each wavelength requires that the power and polarization of each optical pump laser be adjusted and balanced. The process of adjustment and balance of optical pump lasers requires costly logistical support and offers an opportunity for error. Further, additional optical pump lasers increase the chances of optical system failure due to component failure.